Roentgen-ray device.



W. D. CUOLIDGE.

ROENTGEN RAY DEVICE.

APPLICATION Fl'LED'FEB. 5, 1916.

1,253,156, v Patented Jan. 8,1918.

William IlCoolidge,

HIS DTttorneg.

UNITED STATES PATENT OFFICE.

WILLIAM D. GOOLIDGE, OF SCHENECTAIDY, NEW YORK, ASSIGNOB. T0 GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

BOENTGEN-RAY DEVICE.

Specification of Letters Patent.

Patented Jan. 8, 1918.

To all whom it may concern:

Be it known that I, WILLIAM D. Coonrnon, a citizen of the United States,residing at Schenectady, in the county of Schenectady and State of NewYork, have invented certain new and useful Improvements in ltoentgen-RayDevices, of which the followmg 1s a specification.

The present invention comprises an improvement in the construction ofanodes for high powered electron discharge devices, particularly targetsfor X-ray tubes.

Roentgen ray devices are commonly op erated with a variable currentsuch, for example, as derived from the rectification of a high potentialalternating current or when a rectifying tube is used, it may beconnected directly to a transformer. In either case the heat generatedat the target or anode varies in step with the energy input. In theX-ray devices operating by virtue of the ionization of' residual gas,inputs of energy large enough to cause harmful effects because of theintermittent character of the heating can be impressed upon the tube,for time intervals too short to cause damage, say for a second or two,due to 'the excessive heating of the bulb. However, X-ray tubesoperating with a substantially pure electron discharge may be operatedcontinuously without excessive heating of the bulb.

I have found that when an X-ray tube of this type is operatedcontinuously with a relatively large energy input, for example, one ormore kilowatts, that a mechanical disintegration of tearing of the anoderesults which is not observable with low powered apparatus. Myexperiments have shown that this disintegration is the result of themechanical tearing caused by the rapid expansion and contraction takinplace due to the intermittent conveyance 0 heat from the heat receivingface to the cooled section of the anode.

In accordance with my present invention the anode is preserved intact bymaking the energy receiving face of the anode of sufficient thickness toafiord heat storage capacity great enough to transfer the variable heatinput to the actively cooled parts of the metal ata rate nearly uniform.My invent'ion is particularly applicable to an anode comprising a faceplate of highly refractory metal, such as tungsten and a backing ofother metal such, for example, as copper.

' My invention will be more fully described n connect on with theaccompanying drawmg in which Figure 1 "illustrates an X-ray target inperspective; Fig. 2 is a cross-sectional view of the same, Fig. 3illustrates an X-ray tube provided with a target made in accordance withmy invention, and Fig. l is a detail view of a cathode Referring toFigs. 1 and 2 the target illustrated comprises a ray-receiving plate 1consisting of tungsten or other highly refractory metal and a backingtube 2, the end wall 3 of which is in intimate heat-conveying relationto the plate 1. For example, when the end wall 3 0f the cooling deviceconsists of copper, a desired intimate weld may be $8- cured by meltingboronized copper in contact with the tungsten plate in a vacuum asdescribed in my Patent 1,162,341 of November 30th, 1915. The copperplate 3 may then be soldered or welded to the tube 2 in any convenientway, for example, as indicated at 4. A tube 5 supported and centered bylugs 6 serves for the introduction of a cooling fluid, such, forexample, as water. The

target 1 should be relatively thick as com-- pared with face platesheretofore employed in water-cooled X-ray targets. For example, in atube capable of operating with a current of about 0.1 amperes at about50,000 volts with currents of commercial fre uency, for example, cycles,a tungsten p ate of about i" in thickness should be used. With a plateof this thickness the heat delivery to the plate 3 is uniform enough toreduce the tearing or disintegrating efiect of rapid expansion andcontraction of the backing metal, sufiiciently to give the X-ray tube asatisfactory life.

Fig. 3 shows one form of X-ray tube in which a target above describedhas been operated continuously for days at a time without'interruption.The tube comprises the usual glass envelop 7, an electron-emittincathode 8, such as described in the Physic Review for December 1913' anda. watercooled anode 9 of the type above described.

The tube 2 is mounted on an iron tube 10 The cathode filament 16, Fig. 4is'heated by a battery 17 or other convenient low'potential source. The:main current is supplied by a transformer 18, the secondary of which iconnected to the terminals of the Xray tube by the conductors 19, 20. Asdescribed in the above article in the Physical Review, the tube isevacuated to a pressure so low that positive ionization of residual gasis substantially absent or negligible.

When the tube is operated with alternating current any slight amount ofgas evolved from the anode is electrically precipitated by a dischargeemanating from the electrode 9 when acting as cathode for a current Wavenegative with respect thereto, thereby vaporizing or sputtering copper.When a unidirectional current supply is used, the focusing ring 21, Fig.4, about the cathode is c0nstituted of copper, or other readilysputtered metal. Positive ionization of residual constant rate when vicecomprising a member of soft metal offood heat'conductivity, means forcooling said member and a plate of highly refractory metal in intimateheat conveying relation to said member, said plate having a mass Whichwill provide a heat storage capacity sufiiciently great to transfer heatto the soft metal member at a substantially currents of commercialfrequency.

In witness whereof, I have hereunto set my hand this 2nd day ofFebruary, 1916.

WILLIAM D. COOLIDGE.

operated with variable Corrections in Letters Patent No. 1.253, 56.

It is hereby certified that in Letters Patent No. 1,253,156, grantedJanuary 8, 1918, upon the application of William D. Coolidge, ofSchenectady, New York, for an improvement in "Roentgen-Ray Devices,errors appear in the printed specification requiring correction asfollows: Page 1, line 36, for the word of, first occurrence, read or;page 2, line 27, for the word food read good; and that the said LettersPatent should be read with these corrections therein that the sanie mayconform to the record of the casein the Patent Oifice.

Signed and sealed this 12th day of February, A. D., 1918.

[SEAL] J. T. NEWTON,

Commissioner of Patent-x.

